In elevator systems, it has heretofore been general practice to provide a traveling cable between an elevator car and a machine room in order to effect signal transmission between the car and the machine room and also to supply electric power from the machine room to the car. However, it may not be possible to use such a traveling cable in outdoor observation elevators or high rise reclined elevators. For this reason, systems in which no traveling cable is employed to effect signal transmission and supply power between the car and the machine room have been proposed and put into practical use. These prior art systems include a first type in which an elevator car with a battery thereon uses power supplied from the battery for illumination inside the car and for activation of a drive unit for opening and closing the door of the car. An inductive radio is employed to effect signal transmission between the elevator car and the machine room. A second type of conventional system employs trolley wires disposed along the hoistway to supply power and signal transmission between the car and the machine room.
These prior art systems suffer, however, from the following disadvantages.
In the first type of conventional system, the battery that is loaded on the elevator car has the disadvantages of heavy weight, troublesome maintenance, short lifetime, and high cost. In addition, the inductive radio that is employed to effect signal transmission between the car and the machine room is practical only when used for transmission of an operating condition signal, such as a signal for calling the car. It is predicted that the error rate of a serial transmitter is in the range of about 1.times.10.sup.-4 to 1.times.10.sup.-9. Accordingly, the inductive radio is not sufficiently reliable for transmission of safety circuit signals, such as an emergency stop signal generated when an emergency situation occurs or a detection signal representing that the car door is open.
Further, since the frequency band for the inductive radio is restricted to several hundred kHz, it is impossible to transmit a video signal (5 to 6 MHz bandwidth) from a camera provided to monitor the inside of the elevator car.
In the abovementioned second system, since transmission of all signals is effected through trolley wires, it is necessary to provide a number of trolley wires commensurate with the number of floors at which the car needs to stop. Because signal lines for a call button, an answering lamp, and a floor display lamp must be provided for each of the floors, an increase in the number of floors requires a correspondingly increased number cf signal lines. Accordingly, this type of conventional system is practical only where the car must stop at a small number of floors, since the number of trolley wires then will be correspondingly small. With a large number of floors, it may be physically impossible to lay out the correspondingly large number of trolley wires along the hoistway.